1. Field of the Invention
This invention relates generally to traveling grates such as those used in the heat processing of mineral ore as, for example, in the sintering or pelletizing of such ores and, more particularly, to apparatus for adjusting the position of the rails on which the pallets move in order to maintain a proper position of the pallets with respect to each other.
2. Description of the Prior Art
The travelling grate systems as conventionally used in the sintering and pelletizing process have an upper run and a lower run. The particulate material is charged to the grate at a feed zone at the beginning of the upper run, is passed through a treating zone where the material is subjected to heating and possibly cooling and then to a discharge zone where the material is discharged. The discharge zone is usually a transition zone between the upper and the lower runs. The grate then moves along the lower run back to the beginning of the upper run.
In such traveling grate systems, the pallets which include the grate and side members form a channel or pocket where the material being treated is carried. These pallets include wheels which run on trackways of the upper and lower runs. Conventionally, the pallet frames which pass over the machine tracks of each run are pushed from the feed zone to the discharge zone by the upper driving sprocket on the upper run and are returned from the discharge zone to the feed zone by gravity. The discharge zone usually is an arcuate or curved portion which is the transition between the upper and lower runs.
The side members of these pallets are carefully machined so that the sides of one pallet fit the sides of the subsequent and the preceeding pallets to provide a predetermined gap space, called a "pallet gap", between the pallets. Normally, a short gap is required between the push section of the upper zone and the gravity section of the lower zone. This short gap is known in the art as a "pallet track gap".
The traveling grate, being of metal, expands as it is heated and contracts as it is cooled. The length of the pallets change with the temperature and the length of the tracks or runways change with temperature. It is desirable to keep the distance or pallet gap between the pallet sides the same regardless of the operating conditions of the traveling grate, but this is difficult to accomplish, particularly as the condition of the traveling grate changes from a cold start condition to a full, steady start operating condition.
U.S. Pat No. 4,127,381 attempts to solve the problem resulting from temperature changes by placing the pallet drive sprocket on a pivotable lever so that the sprocket position can be changed to compensate for any misalignment of the pallet resulting from temperature changes. U.S. Pat. No. 3,765,525 tries to compensate for the change in temperature by adjusting the location of the shaft bearings, particularly the tail shaft bearing of the grate by way of a hydraulic mechanism so as to compensate for dimensional changes in the chains which drive the conveyor, which dimensional changes are caused by temperature changes to which the traveling grate conveyor is subjected.
As empirical solution has also been used. This solution is to design the length of the track which constitutes the upper and lower runs as long as possible, based upon the theory that the pallets will undergo a greater change with increasing temperatures than will the runway track. Thus, the practice according to this solution has been to space the distance between the pallets for the non-operating or cold conditions; i.e., design the "pallet gap" (the distance between the pallets) at this time deliberately long so that, as the length of the pallets expands with an increase in temperature, the gap between the pallets closes to a desired or acceptable operating gap. A condition employing this empirical solution, conventionally considered to be tolerable, was one in which the gap was satisfactory if the pallets were to be operating at least 90% of the lifetime of the machine in the hot condition. The problem with the empirical solution is that it required the machine to be designed to withstand the severe mechanical forces encountered when the machine was operating under a cold condition as in the start up of the operation.